The present invention relates to machine tools, and more particularly to machine tools having a gate structure.
Machine tools are already widely known which comprise a table supported by a bed for forward and rearward movement, left and right columns arranged upright on opposite sides of the path of movement of the table, a cross rail supported by the columns for upward and downward movement, and a spindle head supported by the cross rail for leftward and rightward movement. A vertical guide rail and a vertical screw rod are provided on the front side of the columns. The rear side of the cross rail is provided with a vertical guide groove having the vertical guide rail slidably fitted therein and with an internally threaded member screwed on the vertical screw rod. The front side of the cross rail is provided with a horizontal guide rail and a horizontal screw rod. The spindle head has a rear side provided with a horizontal guide groove having the horizontal guide rail slidably fitted therein and with an internally threaded member screwed on the horizontal screw rod.
Prior known machine tools become misadjusted following startup due to the creation of plurality of discrete separate unbalanced internal forces created by internal heat generation. Such forces act to distort the geometry of the spindle head support drive and guide means to detrimentally affect the accuracy of the machining function.
More specifically, in prior art devices during the upward and downward movement of the cross rail, the heat generated by the vertical guide rail and the vertical screw rod is released at the front side of each column where it tends to expand that portion of the column. Similarly, leftward and rightward movement of the spindle head results in localized heat generation by the horizontal guide rail and the horizontal screw rod which is also released at the front side of the cross rail. The concentrated heat production at forward portions of the structure consequently causes local deformation of the cross rail or columns which shifts the position of the spindle to impair the accuracy of machining functions of the equipment.
The preferred embodiment of the invention described below is proposed in order to overcome these problems (see, for example, JP-A No. 62-173128).
The present invention employs a unique combination of components oriented and constructed so as to avoid production of unbalanced concentrated heat relative to the cross rail and the columns so as to avoid creation of unbalanced forces which would cause misalignment of the spindle head and result in an inaccurate machining function.